Embryos from BSEcows – thumbs-up

PROGENY derived from embryos recovered from cows suffering BSEare showing a clean bill of health. Thats according to latest results in the long-term MAFF-funded BSE research project being conducted at ADAS High Mowthorpe, Yorkshire.

The experiment involved the implantation of embryos collected from cows actively suffering from BSE into 352 Hereford x Friesian heifers imported from New Zealand, which is BSE-free.

The implants, carried out in l991 and l992, produced 260 embryo transfer offspring, all of which are being retained at Mowthorpe for a minimum of seven years.

All of these progeny had a BSE infected dam and 53% had a BSE positive sire. So far, High Mowthorpe has not experienced a single case of BSE.

But Tony Wrathall, MAFF vet in charge of the project, stresses that this should not be interpreted as an indication that BSE is not reproductively transmitted.

All the embryos collected were at the zona pellucida intact stage (still surrounded by a hard shell) and were washed 10 times to remove any possible external infection. Collection seven days after fertilisation left a lot more reproduction to take place, he explains.

"Because these embryos were collected in the first week of pregnancy, there, of course, remains the remote possibility transmission of BSEfrom dam to offspring could have occurred in the rest of the pregnancy or at parturition."

But the absence of any evidence of BSE in the herd was encouraging, especially for the important export trade in embryos. If the recipient surrogates and their first calf offspring remained negative, it would make the task of assessing the risk of BSE transmission by in vivo derived embryos a lot easier.

All the New Zealand surrogates and their first calf female offspring have gone on to breed naturally within a large single suckling beef herd at Mowthorpe. Steers have been grown slowly on a diet consisting largely of wheat straw.

The aim is to retain all the surrogates and first calf progeny for seven years, allowing that the mean incubation period of the disease is five years. They will then be slaughtered and their brains will be carefully scrutinised for any evidence of BSE lesions.

The first 132 New Zealand surrogates are now within a year of their projected slaughter date, and some of their offspring have less than two years to go.

Final results of the experiment, aimed at showing that embryos flushed from BSE affected cows do not transmit the disease, will not be available until early 2001.